With the drive forward to stuff ever more gears onto rear hubs, it is nice to see SRAM take a step back and create a group with less gears simply because that is what makes the most sense for the application.
The real key to this system is the new 7-speed X-Dome mini-block cassette in a 10-24 range. Most downhill bikes are equipped with road-geared cassettes with something like a 12-26 range and 10 speeds. While this was plenty of range for a downhill bike, the tight gear ratios meant often shifting two or three gears at once to get to the desired ratio.
A similar range, with less gears means bigger jumps between gears and less shifting. Many riders of XX1 and X01 11-speed groups (with the 10-42 cassette) have discovered the same thing, that these larger jumps between gears is actually better suited to the way most people ride. This setup only works with the XD cassette body from the X01 and XX1 11 speed groups.
The rest of the group doesn’t really break any new ground, with most of the technology trickled down from XX1. The downhill carbon crank arms are available with tooth X-Sync narrow/wide rings in 30-38 tooth options, although it looks suspiciously like the carbon crank from the standard X01 group. The X-Horizon rear derailleur uses a “straight parallelogram” design, which keeps the derailleur moving in the vertical plane only to reducing shifting effort and reduce ghost shifting. It sounds hard to explain, but it is pretty simple to see what is going on when seen in person.
The rear derailleur also comes in two cage lengths, short and medium, the longer exists mostly to deal with chain-growth on bikes with substantial chainstay growth on compression, something a standard derailleur is better at. And it almost goes without saying, there a one-way roller bearing clutch to help retain that chain.
The main question I have, which I posed to SRAM and am waiting to hear back: Will downhill riders be able to run this system without a chainguide?
For those riders not ready to drop coin on a new shifter, cassette and derailleur to upgrade to less gears, the X01 downhill derailleur is also available in 10-speed configuration.
The new group will be ready for sale in April 2014.